1. Field of the Invention
The invention relates to a resin-sealed semiconductor device, and more particularly, to a Chip Size Package (CSP) whose mounting area is similar to that of a semiconductor chip contained therein. Further, the invention relates to a resin itself used in the CSP, and a method for manufacturing the CSP using the resin.
2. Description of the Related Art
Recently, since resin-sealed semiconductor devices are applied to memory cards, IC cards and portable telephones, a demand for thinner, smaller and lighter is becoming more and more intense. In response to the demand, shapes or structures of resin-sealed semiconductor devices have been improved. One of the improvements is a Chip Size Package (CSP) type resin-sealed semiconductor device.
Generally, a CSP-type semiconductor device includes a semiconductor chip having integrated circuits on its surface, a plurality of surface electrodes on the surface of the semiconductor chip, an insulating layer formed on the semiconductor chip, projection electrodes formed on the insulating layer, metal wires for connecting the surface electrodes to the projection electrodes, a resin shield for sealing the entire surface of the semiconductor chip, and metal balls formed on the projection electrodes. By a process called dicing, a semiconductor wafer is divided into many CSP-type semiconductor devices after all components are formed on the semiconductor wafer.
As described above, in the process for manufacturing the CSP-type semiconductor device, the resin shield is formed on the semiconductor wafer. During the formation of the resin shield, the semiconductor wafer is heated so as to melt the resin material. Then, the melted resin is flowed on the heated semiconductor wafer, and then solidified.
Thermal expansion coefficients of the resin and the semiconductor wafer are determined by their material. Therefore, when the semiconductor wafer on which the resin shield is formed is cooled to room temperature to solidify the resin material, the resin and the semiconductor wafer either shrink or stretch. In the dicing process for dividing the semiconductor wafer into CSP-type semiconductor devices, the semiconductor wafer is placed on a vacuuming table. However, the semiconductor wafer is warped by the shrinkage or stretching of the resin shield, and as a result, the bottom surface of semiconductor wafer is not in complete contact with the table. Therefore, during the dicing process, the semiconductor wafer is not precisely divided along grid lines.
Further, after a CSP-type semiconductor device is mounted on a board, the device is heated on some occasions. Since the board also has a thermal expansion coefficient which is determined by the material of the board, the board and the CSP-type semiconductor device either shrink or stretch after the board and the device are cooled to room temperature. Because of the differences in thermal expansion coefficient between the board and the CSP-type semiconductor device, the metal balls connecting the CSP-type semiconductor device may crack. Once cracks form in the metal balls, the reliability of the metal balls for performing their connecting function is reduced. Moreover, since the resistance values of the metal balls are increased by the cracks, the reliability of the CSP-type semiconductor devices is reduced.